Synthesis, Structure And Photophysics Properties Of Neutral Cu(Ⅰ) Complexes Containing 1,10-phenanthroline Ligands

In this thesis, two kinds of neutral Cu(I) complexes with substituent 1,10-phenanthroline ligands were synthesized. Their structures were characterized by single crystal X-ray diffraction,1H NMR and infrared spectroscopy. The luminescent properties were determined by UV-Vis absorption spectra, fluorescence spectra, luminescent lifetime and quantum yield measurements. Quantum chemistry calculation was employed to elucidate the luminescence mechanism. Main results in this paper are summarized as follows:1. The ligand 2,9-di-n-butyl-1,10-phenanthroline (dnbp) was synthesized, and a novel neutral dinuclear Cu(I) complex [Cul(dnbp)]2, was prepared by the reaction of Cul and dnbp in tetrahydrofuran solution. Single crystal X-ray diffraction shows that this complex consists of a distorted tetrahedral Cu2I2 core, in which each copper(Ⅰ) ion is linked by two iodo-bridges and a dnbp ligand to form tetrahedron structure. The complex has a low-energy absorption band ranging from 350 nm to 500 nm in dichloromethane solution, which can be assigned to the metal-to-ligand charge transfer (MLCT) transitions. At room-temperature, the complex in the solid state exhibits red phosphorescence with the maximum emission peak at 653 nm. Its emission lifetime is 3.1 p,s, and photoluminescence quantum yield is about 0.013. The luminescence belongs to (M+X)LCT excited state emission.2. Four neutral mononuclear Cu(I) complexes were synthesized based on cuprous halide (Cul or CuBr) and the derivatives of 1,10-phenanthroline with different substituents at its 2 and 9 positions, as well as triphenylphosphine. Single crystal X-ray diffractions demonstrate the tetrahedron structures are formed for all these complexes, among which the complexes with ligand 2,9-di-substituted 1,10-phenanthroline show more regular structures approach to ideal tetrahedron structure. For the complex with methyl or n-butyl substituent, its average lengths of the Cu-N (2.115 A,2.122 A) and Cu-P bonds (2.225 A,2.233 A) are longer than that of the complex with 1,10-phenanthroline (2.096 A,2.198 A), respectively. The geometry of the complex chelating 2,9-dimethyl or 2,9-di-n-butyl 1,10- phenanthroline ligand exhibits a slight flattening distortion in the ground state, because the angles between the plans of N-Cu-N and P-Cu-I are 87.99 and 88.57 degree, respectively. However, for the complex with non-substituted 1,10-phenanthroline, a serious flattening distortion of its structure occurs due to the angle only 81.79 degree. These differences indicate that bulky substituents at 2,9 positions in 1,10-phenanthroline ligand can alleviate the flattening distortion in the ground state. At room-temperature, the non-substituted 1,10-phenanthroline complex shows weak red photoluminescence. In contrast, the 2,9-substituted 1,10-phenanthroline complexes present a significant improvement of the luminescent properties, which exhibit bright orange photoluminescence. Their emission lifetimes are within 10.6-11.3 μs, and photoluminescence quantum yield within 0.43-0.51. The microsecond-scale lifetimes suggest that the luminescence of these complexes can be ascribed to phosphorescence emission.3. Quantum chemistry calculations indicate that the emission of the complexes [CuI(dnbp)(PPh3)] or [CuI(dmp)(PPh3)] is originated from the MLCT state in combination with halogen-to-ligand charge transfer (XLCT) in the excited states. The 2,9-substituted 1,10-phenanthroline complexes show an increase in LUMO energy, so that the gap between their HOMO and LUMO enlarge from 2.3 eV to 2.6 eV, leading to a blue shift of the maximum emission. This also evidences the complex with substituent at 2,9 positions can block the distortion in the excited states. At 10 K, a substantial increase of the photoluminescence quantum yield compared to that of at room-temperature from 0.51 to 0.62 for n-butyl substituted 1,10-phenanthroline complex, as compared with that of from 0.43 to 0.41 for methyl substituted one, indicates long substituent is helpful to inhibit distortion effectively in the excited states and raise photoluminescence quantum yield at low temperature. The radiative constants of the substituted 1,10-phenanthroline complexes from methyl to n-butyl increase from 4.06×104 s-1 to 4.50×104 s-1, while their corresponding non-radiative constants decrease from 5.08×104 s-1 to 4.32×104 s-1 These manifest higher photoluminescence quantum yield for n-butyl substituted complex is originated from both the increase of radiative constant and even the decrease of non-radiative constant due to longer substituents at 2,9 positions for 1,10-phenanthroline complexes.